A method for controlling nail tip defects in vacuum electron beam deep penetration welding

Abstract

The present invention provides a method for controlling nail tip defects in vacuum electron beam deep penetration welding, which relates to the technical field of metal material welding and is used to form a weld that is closed at both ends, comprising S1, placing a workpiece to be welded on a tool and fixing it; S2, determining the position of a region to be welded, adjusting the position of an electron gun so that it is directly opposite to the region to be welded and the distance between the electron gun and the workpiece to be welded is 400-800 mm; S3, evacuating the vacuum to a vacuum degree of ≤5×10 ‑2 After Pa, the electron beam welder is boosted to 120-150KV, and welding is performed according to a preset waveform, wherein the preset waveform is a double elliptical composite waveform, and the focusing current is set to 2400-2450mA at the lower focus position; S4, cooling to below 100°C and opening the vent valve to remove the workpiece. The method for controlling nail tip defects in vacuum electron beam deep penetration welding of the present invention realizes the control of nail tip defects in the arc closing zone of electron beam deep penetration welding, greatly reduces the degree and number of nail tip defects by 70-90%, and can be used for ultra-large thick plates, especially for good internal forming control of annular workpieces in electron beam welding.

Description

Technical Field

[0001] The invention relates to the technical field of metal material welding, and in particular to a method for controlling nail tip defects in vacuum electron beam deep penetration welding. Background Art

[0002] Vacuum electron beam welding applies high voltage between the cathode and the anode, focuses through a magnetic lens, and deflects the electron beam generated by the secondary focusing coil and bombards the surface of the workpiece in a vacuum, rapidly converting the kinetic energy of the electrons into heat energy to melt the metal of the workpiece for welding. It has the advantages of a large weld depth-to-width ratio (10-50:1), a small heat-affected zone, good organizational properties, and easy computer control. It has been widely used in precision technology, aerospace, and other fields.

[0003] Since the electron beam can form a small beam spot on the workpiece surface and the welding speed is fast, it is easy to form a top defect at the root of the formed molten pool, specifically poor root fusion and large fluctuations in the depth of fusion. To this end, the Chinese patent application number 202111330004.2 discloses an electron beam welding method for ultra-high strength gear bearing steel, including: S1. Grinding and rust removal of the welding surface and the surrounding 20mm area of ​​two welding plates with a specification thickness of 5-15mm, and then using non-woven fabric dipped in acetone to wipe the welding surface and the surrounding area, and arc starting blocks and arc closing blocks are respectively provided on both sides of the welding seam to be welded; S2. Use the "Ⅰ" type flat plate docking method to place the two welding plates on the vacuum chamber platform of the electron beam welding equipment for fixing; S3. Evacuate the vacuum chamber, and when the vacuum pressure reaches 5×10 -2 After Pa, find the position trajectory of the weld to be welded and perform electron beam welding. The welding process parameters are: welding speed is 2-6mm / s, welding acceleration voltage is 70-100kV, welding focus current is 1200-1600mA, and electron beam current is 5-30mA; S4, after welding, keep the vacuum chamber in vacuum for 10-20min, and then vent and take out of the furnace. This scheme sets an arc starting block to guide the nail tip defects caused by the fluctuation of electron beam energy to the arc starting block for removal to ensure that the structural parts have no excessive welding defects within the effective penetration depth and length range; but the arc starting block can only be set for open workpiece structures, and it will significantly increase the workload of welding and processing.

[0004] For thick closed annular structural parts, the structure itself cannot be equipped with an arc-starting block; although the full-thickness penetration welding process can effectively control the root nail tip defect, the energy attenuation and fluctuation in the arc closing area will increase the instability of the molten pool, causing unavoidable nail tip defects, which will seriously affect the weld quality and structural stability of the joint.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The problem solved by the invention is that nail tip defects are easily generated in the arc closing area when vacuum electron beam deep penetration welding is used to form a closed weld.

[0007] In order to solve the above problems, the present invention provides a method for controlling nail tip defects in vacuum electron beam deep penetration welding, comprising:

[0008] S1. Place the workpiece to be welded on the fixture and fix it, ensuring that the joint assembly gap is ≤0.2mm and the misalignment is ≤0.3mm;

[0009] S2. Determine the position of the area to be welded by using the CCD observation system and adjust the electron gun to face the area to be welded and the distance between the electron gun and the workpiece to be welded is 400-800mm;

[0010] S3, evacuate to a vacuum degree of ≤1×10 -2 After Pa, the electron beam welder is boosted to 150KV, and welding is performed according to a preset waveform, wherein the preset waveform is a double elliptical composite waveform, the welding speed is 100-200mm / min, the electron beam current is 250-350mA, the lower focus focusing current is 2400-2450mA, the amplitude X=2-3mm, Y=1-2mm, and the frequency is 1000-3000HZ;

[0011] S4. Cool down to below 100℃ and open the vent valve to remove the workpiece.

[0012] The present invention controls the electron beam welding action track and the energy distribution of the molten pool by loading the electron beam welding vector scanning graphics, stabilizes the molten pool keyhole state during the arc closing process of the electron beam deep penetration welding, and regulates the smooth transition of the metal vapor escape channel and the keyhole at the root of the weld, thereby eliminating the large fluctuation of the nail tip defect, realizing the formation of the deep penetration welding weld of the thick plate, and controlling the large fluctuation of the nail tip defect, thereby improving the formation and quality of the weld. Preferably, the workpiece to be welded is a titanium alloy.

[0013] Preferably, the preset waveform is a composite waveform composed of a first ellipse and a second ellipse, wherein the expression of the first ellipse is: , where a1 and b1 are the major and minor semi-axis of the first ellipse, respectively, and the expression of the second ellipse is , where a2 and b2 are the major and minor axes of the second ellipse respectively, where the value of a1:b1 is 2-3; the value of a2:b2 is 2-3, the value of a1:a2 is 2-3, and the value of b1:b2 is 2-3; the energies of the first ellipse and the second ellipse are Q1 and Q2 respectively, where Q1:Q2=4-6:1.

[0014] Preferably, the preset waveform is a composite waveform consisting of a first ellipse and a second ellipse, wherein the first

[0015] The expression of an ellipse is , where a1 and b1 are the major and minor semi-axis of the first ellipse, respectively, and the expression of the second ellipse is , where a2 and b2 are the major and minor axes of the second ellipse respectively, where a1:b1=a2:b2, a1:a2=b1:b2; the energies of the first ellipse and the second ellipse are Q1 and Q2 respectively, where Q1:Q2=4-6:1.

[0016] Preferably, the major semi-axis from the first ellipse to the second ellipse is the same as the welding direction of the vacuum electron beam. In other words, the electron beam alternates along the trajectory formed by the first ellipse and the second ellipse, the first ellipse and the second ellipse intersect at a point, and the intersection point is located on the weld formed by the vacuum electron beam.

[0017] Preferably, the welding method further comprises: S0, mechanically treating the surface of the workpiece to be welded, and then ultrasonically cleaning it with acetone and alcohol solvent respectively to remove oil stains.

[0018] Preferably, the workpiece to be welded is an annular or rectangular workpiece and forms a closed weld after welding, and the thickness of the workpiece to be welded is h≥80 mm.

[0019] Compared with the prior art, the method for controlling nail tip defects in vacuum electron beam deep penetration welding described in the embodiment of the present invention has the following beneficial effects: 1) The present invention controls the motion trajectory and energy distribution of the weld acted on by the electron beam to change the motion state of the molten pool in the weld area, thereby reducing 70-90% of the top defects and obtaining a joint with good internal quality of the weld; 2) The present invention can ensure good forming of the front and back sides of the weld, effectively improve the one-time weld qualification rate of the joint, improve welding efficiency and ensure reliable quality; 3) It is conducive to the continuous completion of the arc starting and arc ending actions of electron beam welding in a closed annular structure at one time; if the weld has internal defects beyond the acceptance criteria, remelting and repair welding can be performed according to the original welding parameters, providing an electron beam repair welding process, reducing the risk of repair welding, and having direct guiding significance for actual engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a preset waveform of an electron beam according to Embodiment 1 of the present invention;

[0021] Figure 2 This is an appearance diagram of welds formed by the welding methods of Example 1 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. The technical features of the embodiments of the present invention can be combined with each other without conflict.

[0023] The high-power vacuum electron beam welding of thick plate (δ>80mm) metal materials can penetrate and obtain a large thickness penetration at one time, which has a very significant advantage in achieving high-quality and high-efficiency welding of large penetration welds. For thick closed annular structural parts, the full-thickness penetration welding process can effectively control the root nail tip defects, but the energy attenuation and fluctuation in the arc closing zone of electron beam welding will increase the instability of the molten pool, causing unavoidable nail tip defects, which will seriously affect the weld quality and structural stability of the joint. To this end, the applicant proposes the following technical solution.

[0024] Example 1

[0025] A method for controlling nail tip defects in vacuum electron beam deep penetration welding, comprising:

[0026] S1. Use a wire brush to grind the surface of the workpiece to be welded until a bright metallic luster appears on the surface for mechanical treatment, and then use acetone and alcohol solvents for ultrasonic cleaning to remove oil stains.

[0027] S2. Place two annular workpieces to be welded (outer diameter 2m, thickness 100mm, height 500mm) on the fixture and fix them, ensuring that the joint assembly gap is ≤0.2mm and the misalignment is ≤0.3mm;

[0028] S3, determine the position of the area to be welded by using the CCD observation system and adjust the electron gun to face the area to be welded and the distance between the electron gun and the workpiece to be welded is 400 mm;

[0029] S4, evacuate to a vacuum degree of ≤5×10 -2 After Pa, the electron beam welder was boosted to 150KV, and welding was performed according to the preset waveform, with a welding speed of 100mm / min, an electron beam current of 250mA, a lower focus current of 2400mA, a preset double elliptical scanning waveform, a scanning amplitude of X=2mm, Y=1mm, and a scanning frequency of 2000HZ;

[0030] The preset waveform is a composite waveform composed of a first ellipse and a second ellipse, wherein the expression of the first ellipse is: , where a1 and b1 are the major and minor semi-axis of the first ellipse, respectively, and the expression of the second ellipse is , where a2 and b2 are the major and minor axes of the second ellipse, respectively, where a1=3, b1=1, a2=1.5, b2=0.5; the energies of the first ellipse and the second ellipse are Q1 and Q2, respectively, where Q1:Q2=5:1;

[0031] The preset waveform can be adjusted proportionally according to metal materials of different thicknesses and materials, with extremely high flexibility.

[0032] S5. Cool down to below 80℃ and open the vent valve to remove the workpiece.

[0033] The present invention utilizes electron beam vector deflection scanning to control welding trajectory and energy distribution, and changes the keyhole flow state of the molten pool stirring in the weld zone during welding, thereby delaying the solidification speed of the molten pool root, greatly eliminating the nail tip defects in the arc closing zone of thick plate electron beam welding, giving full play to the high-quality and efficient welding advantages of thick plate electron beam deep fusion welding, realizing the control of nail tip defects in the arc closing zone of electron beam deep fusion welding, and greatly reducing the degree and number of nail tip defects by 70-90%, providing a new technical process for vacuum electron beam welding of large-thickness structural parts in the future, having broad application prospects, and being able to be used for good internal forming control of ultra-large thick plate electron beam welding, so as to realize efficient and reliable welding research and development of products.

[0034] Comparative Example 1

[0035] Welding is performed according to the scheme of Example 1, with the only difference being that the preset waveform in step S4 is circular, the scanning amplitude is X=2mm, Y=1mm, and the scanning frequency is 2000HZ.

[0036] The welds formed by vacuum electron beam welding in Example 1 and Comparative Example 1 were tested using an X-ray flaw detector and ultrasonic testing. The results are shown in Figure 1 The results show that the weld in Example 1 meets NB / T47013 Level I and the weld quality is qualified. The welded specimens were sampled and tested, and the joint structure was analyzed using a metallographic microscope. The weld was cut along the center of the weld to observe that the weld quality inside the weld joint and the arc closing area was excellent, and the nail tip defect was greatly controlled.

[0037] The present invention can load an electron beam welding vector deflection scanning graph to increase a double elliptical composite function with amplitudes in the X and Y directions during electron beam welding, thereby achieving the composite of the weld affected by the beam within a unit time, intensifying the deep melting and stirring effect of the electron beam molten pool, and controlling the weld nail tip defect; the beam stays at the same point on the weld for a longer time, the weld root width increases significantly, and the single-point melting time at the weld position is extended in a manner that is beneficial to the overflow of steam at the weld root and the backfilling of molten metal; at the same time, in the arc closing section of thick plate electron beam welding, the molten pool pulse fluctuation caused by the electron beam energy attenuation can be greatly stabilized, which is more beneficial to the control of the nail tip defect in the weld arc closing section.

[0038] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for controlling nail tip defects in vacuum electron beam deep penetration welding, characterized in that: Used to form welds that are closed end to end, including: S1. Place the workpiece to be welded on the tooling and fix it, ensuring that the butt assembly gap is ≤0.2mm and the misalignment is ≤0.3mm. The workpiece to be welded is an annular or rectangular workpiece with a thickness of h≥80mm; S2. Determine the position of the area to be welded by using the CCD observation system, and adjust the position of the electron gun so that it is facing the area to be welded and the distance between it and the workpiece to be welded is 400-800mm; S3, evacuate to a vacuum degree of ≤5×10 -2 After Pa, the electron beam welder is boosted to 120-150KV, and welding is performed according to a preset waveform, wherein the preset waveform is a double elliptical composite waveform, the welding speed is 100-200mm / min, the electron beam current is 250-350mA, the lower focus focusing current is 2400-2450mA, the amplitude X=2-3mm, Y=1-2mm, and the frequency is 1000-3000HZ; The preset waveform is a composite waveform composed of a first ellipse and a second ellipse, wherein the expression of the first ellipse is: , where a1 and b1 are the The major and minor axes, the expressions of the second ellipse are: , where a2, b2 are respectively the major semi-axis and minor semi-axis of the second ellipse, wherein the value of a1:b1 is 2-3; the value of a2:b2 is 2-3, the value of a1:a2 is 2-3, the value of b1:b2 is 2-3; the energy of the first ellipse and the second ellipse are Q1 and Q2 respectively, wherein Q1:Q2=4-6:1; the major semi-axis pointing from the first ellipse to the second ellipse is the same as the welding direction of the vacuum electron beam, the electron beam alternates along the trajectory formed by the first ellipse and the second ellipse, the first ellipse and the second ellipse intersect at a point, and the intersection point is located on the weld formed by the vacuum electron beam, and the second ellipse is located in the first ellipse; S4. After welding, keep the vacuum chamber in vacuum for 10-40 minutes to cool to below 100℃, and then vent and take out of the furnace.

2. The method for controlling nail tip defects in vacuum electron beam deep penetration welding according to claim 1, characterized in that: Also includes: S0. The surface of the workpiece to be welded will be mechanically treated, and then ultrasonically cleaned with acetone and alcohol solvents to remove oil stains.

3. The method for controlling nail tip defects in vacuum electron beam deep penetration welding according to claim 2, characterized in that: The mechanical treatment in step S0 is polishing with a wire brush until a bright metallic luster appears on the surface.

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